Hello everyone, im another new member who has been reading for weeks but only just joined.
I have a scenario that I would like peoples opinions on, I am trying to play devils advocate but am finding it a little tricky.

Im afraid its going to be a long post.
Background is that I grew up as a step child, when I was 7 I chose to move from my BMs to my BFs and moved from being an only child to being the youngest of 5 children. Both of my parents had previously fought for custody but felt that since I was of an age that I could state my reasoning then my wants should be taken into account. That being said they didnt expect it to be permanent but it was.
Fast forward and I am now a step mother but I have been very fortunate to have endured no drama with my step childs BM as both parties have stuck to the CO.
However, my step sisters is a step mother and a bio-mother. She is SM to a 7 year old girl and BM to a 2 year old girl, her partners previous marriage ended on account of his ex wives infidelity, soon after they separated she found out she was pregnant. Yes you can guess ahead she first stated the baby wasnt his, then once the baby arrived said it was. Naturally my sister and her partner said if there was a question of paternity he wanted a DNA, which the mother refused, and be it for right or wrong reasons my sister and her partner decided to leave it and continued with contact for the daughter (who was then just 3 years old). Two years go by with contact issues and custody battles for the daughter, but the potential son is pretty much ignored, the daughters BM uses it as reasoning why she started preventing contact so they all go to mediation etc etc but it continues to break down.
Then my sister has a baby so is in a position whereby shes SM to one definately, one maybe but people are refusing and delaying DNA and BM to one. Theres alot of drama and alot of threats, gameplaying and nastiness from the BM of the two children. Within all the drama the little girl who was then 5 years old states that her BMs boyfriend had hit her...childrens services gets involved, 5 year old says she doesnt want to live with her BM anymore because of abuse etc but the unclear paternity of the baby boy seems to cause some delay.
Along the way the courts make comments about my sister should be doing less in terms of time spent caring for the daughter as the visitation was for the BF and the child herself stated that she doesnt always get to see her BF.
Now fast forward again and the courts finally got both parties to consent to the DNA and low and behold the baby boy is my sisters boyfriends. Which means he is a BF to a 7 year old girl and a now 4 year old son, A 4 YEAR OLD who he has never seen. Oh, along with the now 2 year old he has with my sister.
However the BM has told the 4 year old so many things about his BF that the child is now terrified of him and doesnt want to see him, apparently the courts at this point are not going to inforce it due to the obvious upset to the child.
My sister and her partner were both still fighting for custody of SD 8 when SD8s behaviour suddenly changed, she became very jealous of her half sister and started hurting her and at the point that my sister was working on improving her behaviour, along with her schooling since she is behind at school, SD8 then accuses my sister of abuse (the same as she had said about BMs boyfriend previously) At that point my sister completely disengaged, she was utterly devastated that after so many years of doing nice things, making the effort etc that it had come down to this.
From the time that my sister disengaged her partner didnt really change, or as far as Im aware he didnt. Now SD8 has told them that she doesnt want to see them ever again, that she has only been there because they take her to see people she likes and they give her presents.
Soooo....my sister and her partner have agreed to this, they explained to her that they wouldnt be seeing her for a long time, which SD8 was fine with, she wanted to know which toys she could take back to her mothers, climbed into her BMs car and off she went.
Sisters boyfriend is still in contact with the BM via text to make sure all is ok but its now been TWO months and SD8 is apparently happier and has no inclination of wanting to see them, however does still have contact with her grandparents (from her dads side).
WIthin all of this there is also that 4 year old boy who to this day has never met his father.

6 months ago I moved abroad so I have not been involved with any of them since then other than via the internet but when I first heard all of this I was outraged and disappointed in both my sister and her partner. I had always felt that my sister had been left to do too much and that her partner hadnt stepped up, to me it was a completely ridiculous to have taken 4 years for a DNA. To me they should have paid for it themselves at the start rather than let it get so far.
But after a while I started to wonder whether it was really fair to be so harsh, yes I think they have made mistakes over the time but who hasnt? Yes I think they should have done more but how long can you hold past mistakes over someone?
And when I have grown up with the belief that once a child is old enough to express their opinions and wants in a rational manner and can give reasons as to why then their opinions need to be taken into account. I chose to move when I was the same age as my sisters SD, and I then chose not to see my own BM for a number of months, but Im finding it really hard to understand why they are willing to walk out of two childrens lives.

Thoughts?